Process of producing initiating composition containing lead azide



Patented Sept 29, 1953 BEST AVAILABLE COPY UNITED STATES ATENT OFFICE PROCESS OF PRODUCING INITIATING CO1- POSITION CONTAINING LEAD AZIDE Leon Rubenstein, Saltcoats, Scotland, assignor to Imperial Chemical Industries Limited, a corporation of Great Britain No Drawing.

Application October 16, 1951, Se-

, rial No. 251,627. In Great Britain December '7 Claims.

azide is commonly employed in detonators as the primary initiating explosive whose detonation induces the detonation of the less sensitive secondary explosive charge in the detonator, for example, tetryl or pentaerythritol tetranitrate. Lead azide, the precipitation of which from lead nitrate and sodium azide solutions is frequently conducted in presence of dextrine in order to diminish the liability to spontaneous explosions, is however, insufficiently sensitive to ignition by flame to ignite from the spit of a safety fuse or from an electric fusehead, and it is also lacking in the capacity for cohering when compressed into the detonator tube. It is therefore usual to employ it in admixture with lead styphnate, which has excellent capacity for ignition and is capable when ignited of causing the detonation of the lead az'ide and also enables the composition when compressed to cohere. It is also usual to include minor proportions of tetryl and of aluminium powder in the composition, since the tetryl still further increases the binding properties of the composition and the aluminium serves as a press lubricant and aids inspection. Lead styphnate, however, is extremely sensitive to ignition by electrostatic charges and this constitutes a certain hazard in its own manufacture and that of the initiating composition containing it.

It has been proposed to prepare compositions for blasting detonators characterised by the fact that combinations of lead styphnate and lead azide are produced by graduall running together solutions of readily soluble salts ofstyphnic acid and hydrazoic acid with solutions of soluble lead salts, but the products obtained are heterogeneous mixtures and tend to cake on dry ing giving products of poor running properties,

' and poor ignition and initiating characteristics.

In general, co-precipitation of lead azide with other lead salts of nitrophenolic compounds having deflagrating properties has also hitherto failed to provide useful primary initiating compositions.

I have found, however, that a coprecipitated initiating composition of homogeneous appearinitiating properties, comprising acompound can be obtained by precipitation by mixing a solution of a water soluble normal lead salt of a monobasic acid and an aqueous solution containing a salt of hydrazoic acid and both a normal 2:4 dinitroresorcinate and an acid 2:4 dinitroresorcinate of a cation having a soluble azide.

According to the present invention the method for the production of an initiating composition comprising a major proportion of lead azide and a minor proportion of a normal lead azide salt of a dinitrophenol comprises forming a precipitate by mixing an aqueous solution of a Water soluble normal lead salt of a monobasic acid with an aqueous solution containing a salt of hydrazoic acid as Well as a normal and an acid 2:4 dinitroresorcinate of a cation having a soluble azide.

An initiating composition according to the invention consists of aggregates comprising a major proportion of lead azide and a minor proportion of a normal lead salt of 2:4 dinitroresorcinol.

Sodium azide and the sodium normal and acid salts of 2:4 dinitroresorcinol are preferred but the corresponding magnesium salts of 2:4 dinitroresorcinol may be used.

The amount of the acid salt of 2:4 dinitroresorcinol should be at least {-0- of the amount of the normal salt of 2:4 dinitroresorcinol, and the amount of the water soluble lead salt of the monobasic acid with which the precipitation is carried out should be chemically equivalent to the amounts of azide and of both the aforesaid salts of 2:4 dinitroresorcinol calculated on the assumption that both of the latter are capable of reacting with the water soluble lead salt of the monobasic acid to form normal lead 2:4 dinitroresorcinate. As the soluble normal lead salt of monobasic acid it is preferred to use lead nitrate; but lead acetate may alternatively be used.

It is preferred to carry outthe precipitation at a temperature between 55? and C. by adding relatively concentrated solutions of the two reacting solutions to a large bulk of water.

It is also preferred to carry out the precipitation in presence of a very small proportion of dextrine (preferably 0.01-0.025% calculated on the total weight of the water) The'precipitation is also preferably carried out in the presence of a small proportion of Rochelle salt (sodium potassium tartrate tetrahydrate) in addition to the dextrine. The amount of Rochelle saltmay advantageously be from 015-075 of the weight of the soluble salt of hydrazoic acid used and it is preferably employed in the solution con- .2 taining the salt of hydrazoic acid and the salts of 2:4 dinitroresorcinol.

In the absence of dextrine it has been observed that the ignitibility of the product of the co-precipitationis satisfactory if the precipitation is carried out in such a manner that from the start to the end of the operation there is a progressive change in the appearance of the reaction mix ture, namely that an initially fine yellow turbid.-

ity gives place to fine yellow .to brown precipi= tate and on further addition of the precipitant solution a transformation of both the precipitate and the mother liquor to a-reddish colour, where- I as if the precipitation is carried out under conditions where the last mentioned transformation is not markedly developed, the ignitibility of the.

resulting co-precipitated product is less satisfactory.' The use of the aforesaid small proportion of dextrine is favourable to the full development to the aforesaid'visual appearances and assists in the production of a material of satisfactory ignitibility. Further it has a slight beneficial ef feet in reducing the sensitiveness of the dry prodnot to electrostatic ignition. The presence of the Rochelle salt in the precipitation in addition to the dextrine further improves the ignitibility of the product and very substantially reduces its 'sensitiveness to electrostatic ignition.

It has been observed that the use of an excessive amount of dextrine e. g. of the weight Example I 125 cc. of a sodium salt aqueous solution containing 7.8 g. sodium azide and 3 g. 2:4 dinitroresorcinol that has been reacted with 1.12 g. so-

dium hydroxide in presence of some of the water,

and 0.02 g. Rochelle salt (sodium potassium tartrate tetrahydrate), and the same volume of a solution containing g. lead nitrate in water are delivered simultaneously at a constant rate during 9 minutes into a stirred solution of dextrine in 800 cc. water, the strength of which is 0.02% by weight. The temperature is maintained at 70 C. during the addition of the reagents. After a short lag a yellow turbidity appears, followed by'a yellow to brown precipitate and finally the whole reaction mixture turns red, both precipitate and liquor. The reaction mixture is cooled and the red granular product is collected by filtration, washed with water and dried off in warm air. It is composed of rounded or oval particles, the flowing properties are good, and the minimum weight of the material required for complete initiation of tetryl in a detonator is 0.11 g. compared with 0.18-0.20 g. for an initiating explosive consisting of a mixture of 64.8% lead azide, 27.8% lead styphnate, 2.8% aluminium powder and 4.6% tetryl.

The ignitibility of the material in a detonator is determined by leaving a known gap between the composition and a safety fuse crimpedinto a detonator and finding the proportion of ignitions from the fuse over the gap. In this test the coprecipitate gives similar results to those of the aforesaid composition containing lead styphnate.

l Its cohesive properties under compression are much superior.

In respect of electrostatic sensitivity, the coprecipitate is found to require a critical electrostatic energy discharge of 200,000-470,000 ergs, according to the capacity of the condenser delivering this energy, to efiect ignition. A similar test conducted on lead styphnate which is electrostatically the most sensitive ingredient of the aforesaid composition containing it requires 34:0 ergs.

Example II The preparation of the co-precipitate is conducted as in Example I except that the 125 cc. of solution containing the sodium azide and the normal and acid sodium salts of 2:4 dinitroresorcinol contains 0.012 g. Rochelle salt, while the 800 cc. dextrine solution is of 0.015% concentration. The reaction proceeds in a similar manner to that of Example I, and'the product has good running properties.

A minimum charge of 0.09 g. is required for initiation of tetryl in a detonator. The ignitibility is again similar to that of the aforesaid lead azide, lead styphnate, aluminium, tetryl composition, and for electrostatic discharge the critical energy value ranges from 1'?4,000-865,000 ergs compared with about 250 ergs for a sample of lead styphnate tested at the same time.

Example III Two aqueous solutions each of 500 cc. volume, one containing 31.2 g. sodium azide, 12 g. 2:4 dinitroresorcinol, 4.46 g. sodium hydroxide, and 0.07 g. Rochelle salt, and the other containing 100 g. lead nitrate are added simultaneously at a constant rate over 23 minutes to 3.2 litres of a 0.018% (by weight) dextrine solution, while maintaining the temperature at 70 C. Changes similar to those described in Example I occur during the reaction, and the co-precipitated product is obtained in 94% 0f the theoretical yield (based on the usage of sodium azide, lead nitrate and dinitroresorcinol) and consists of almost circular or oval particles. The material has good flow properties and as a primary initiator for a base charge of tetryl, 0.12 g. of it is required. The cohesive properties of the co-precipitate when pressed in a detonator are far superior to those of the aforesaid composition con taining lead styphnate, while the ignitibility is similar. The electrostatic energy discharges necessary to ignite the material are of the order of a million ergs.

What I claim is:

1. A method for the production of an initiating composition comprising a major proportion of lead azide and a minor proportion of a normal lead salt of dinitroresorcinol which comprises forming a precipitate by mixing an aqueous solution of a water-soluble normal lead salt of a monobasic acid with an aqueous solution containing a salt of hydrazoic acid as well as a normal and an acid salt of 2:4 dinitroresorcinol of which the cation has a soluble azide, the said acid salt of 2:4 dinitroresorcinol being present in amount at least 6 of that of the normal salt of 2:4 dinitroresorcinol and, the said mixing being carried out in the presence of dextrin in amount of from about 0.01% to 0.025% by weight of water present,

2. A method as claimed in claim 1 wherein the salt of hydrazoic acid is sodium azide.

3. A method as claimed in claim 1 wherein the 5 cation of the salts of 2:4 dinitroresorcinol having a soluble azide is sodium.

4. A method as claimed in claim 1 wherein the amount of water soluble lead salt of the monoba-sic acid is chemically equivalent to the amounts of azide and of both of the said salts of 2:4 dinitroresorcinol calculated on the assumption that both of the latter are capable of reacting with the water soluble lead salt of the monobasic acid to form normal lead 2:4 dinitroresorcinate.

5. A method as claimed in claim 1 wherein the soluble normal lead salt of a monobasic acid is lead nitrate.

6. A method as claimed in claim 1 wherein the precipitate is formed at a temperature between precipitation is carried out in the presence of Rochelle salt present in an amount of 0.15 to 0.75% of the weight of the soluble salt of hydrazoic acid used.

LEON RUBENSTEIN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 10 1,552,836 Friederich Sept. 8, 1925 FOREIGN PATENTS Number Country Date 616,456 Great Britain Jan. 21, 1949 OTHER REFERENCES The Chemistry of Powder and Explosives by T. L. Davis. vol. 11, John Wiley and Sons Inc., N. Y., 1943, page 425. (Copy in Div. 70.) 

1. A METHOD FOR THE PRODUCTION OF AN INITIATING COMPOSITION COMPRISING A MAJOR PROPORTION OF LEAD AZIDE AND A MINOR PROPORTION OF A NORMAL LEAD SALT OF DINITROTESORCINOL WHICH COMPRISES FORMING A PRECIPITATE BY MIXING AN AQUEOUS SOLUTION OF A WATER-SOLUBLE NORMAL LEAD SALT OF A MONOBASIC ACID WITH AN AQUEOUS SOLUTION CONTAINING A SALT OF HYDRAZOIC ACID AS WELL AS A NORMAL AND AN ACID SALT OF 2:4 DINITRORESORCINOL OF WHICH THE CATION HAS A SOLUBLE AZIDE, THE SAID ACID SALT OF 2:4 DINITRORESORCINOL BEING PRESENT IN AMOUNT AT LEAST 1/10 OF THAT OF THE NORMAL SALT OF 2:4 DINITRORSORCINOL AND THE SAID MIXING BEING CARRIED OUT IN THE PRESENCE OF DEXTRIN IN AMOUNT OF FROM ABOUT 0.01% TO 0.025% BY WEIGHT OF WATER PRESENT. 